1. Field of Invention
The invention relates to the fabrication of semiconductor wafers, and more especially to wafer cleaning processes that take place during fabrication. These processes generally entail contacting the wafers with chemicals that may be corrosive and hazardous, and then rinsing and drying the cleaned wafer surfaces either to produce a final product, or to enable further fabrication steps.
2. Description of the Related Art
In the fabrication of semiconductor devices, a disc-shaped silicon wafer is subjected to a variety of technologies to create layered structures of semiconductors on its surface. At various stages during this fabrication, the wafer must be subjected to polishing for planarization and to remove surface defects, and post-polishing cleaning before additional structures can be formed on each semiconductor of the wafer. Absent such cleaning, residual contaminants on the wafer surface would preclude the manufacture of modern, highly miniaturized, integrated circuit semiconductor structures.
Polishing for planarizing structure on the wafer surface and removing surface defects often utilizes a chemical slurry in conjunction with a polishing pad for polishing the wafer surface. Such slurry-assisted polishing is referred to as xe2x80x9cchemical mechanical polishingxe2x80x9d or xe2x80x9cCMPxe2x80x9d. Where the polishing is carried out using CMP, or another technique, a polished surface will be contaminated with fine particulates (from the slurry or produced by polishing) and other minute contaminants that must be removed to prevent potential for interference with electrical circuitry being formed on the wafer. Accordingly, after polishing the semiconductor wafers undergo a surface cleaning process, utilizing aggressive chemicals to remove contaminants, followed by rinsing to remove any chemicals and residue, and finally a drying stage to remove rinse fluids. After drying, the cleaned wafers may be subjected to additional fabrication steps.
At the present time, the cleaning and rinsing stages of semiconductor fabrication results in the generation of large volumes of chemical solutions and contaminated water that must be treated for disposal. The chemicals, in particular, do not only pose an environmental hazard, as determined by the United States Environmental Protection Agency (EPA), but also represents a significant additional operating cost in the fabrication of semiconductor wafers. There exists a need to reduce the amount of waste generated for disposal, both for environmental and cost reasons. Notwithstanding, current technology fails to address this need. Moreover, current technology requires separate containers for cleaning and for rinsing the wafers thereby necessitating wafer transfer from one apparatus to another. Such handling poses risk of wafer damage and also increases the overall time for the cleaning/rinsing operation. Accordingly, a process that reduces wafer handling and the time for cleaning and rinsing would present significant advantages. Additionally, if such processes could be carried out on a single station, with a relatively small xe2x80x9cfootprintxe2x80x9d that requires less space than current apparatus, then it would present further advantages in the more efficient use of expensive space in the fabrication environment. Desirably, the single station should also be self contained in the sense of not emitting particles to its surroundings that could contaminate its environment and other fabrication processes.
The invention provides a unique apparatus for the cleaning and rinsing of disc-shaped substrates, such as silicon wafers, high precision lenses, and the like. This Summary of the Invention section is intended to introduce the reader to aspects of the invention and is not a complete description of the invention. Particular aspects of the invention are pointed out in other sections here below and the invention is set forth in the appended claims, which alone demarcate its scope.
In one aspect of the invention, there is provided a method of cleaning and rinsing the disc-shaped substrates in a single chamber, albeit that the invention is not limited to using a single chamber. The method includes cleaning surfaces of a plurality of disc-shaped substrates in the chamber with a cleaning solution, and rapidly removing the chemical cleaning solution from the chamber. During the process, the disc-shaped substrates are also rinsed with a rinsing liquid, that is likewise rapidly removed from the chamber, preferably under gravity.
In another aspect of the invention, there is presented a method for cleaning disc-shaped substrates and reusing cleaning solutions to minimize the generation of chemical wastes. This method includes immersing a plurality of disc-shaped substrates in a chemical cleaning solution, for a sufficient time to provide cleaning action. The cleaning solution is then dumped to a holding tank. Solution from the holding tank is filtered and analyzed for chemical properties. Depending upon the analysis, a portion of the chemical solution may be routed to disposal, and fresh chemical solutions may be added until the analysis of the chemical solution is within a required range of specification. The chemical solution may then be recycled for reuse in cleaning other substrates.
In another aspect of the invention, there is a method of cleaning, rinsing and drying batches of disc-shaped substrates in a single chamber. The method may use recycled chemical cleaning solution or may use fresh chemical cleaning solution. In accordance with the method, a plurality of disc-shaped substrates is cleaned in the chemical solution in a cleaning chamber. After cleaning the substrates, the chemical cleaning solution is dumped from the chamber, filtered and analyzed. The method includes rinsing the substrates in the chamber with a rinse liquid, and dumping the rinse liquid from the chamber after rinsing. The rinsed substrates are dried in the cleaning chamber, and the dried substrates are then removed from the chamber and replaced with a second plurality of substrates. Preferably, this second plurality of substrates is cleaned with recycled chemical cleaning solution that comprises at least a portion of the dumped, filtered and analyzed solution used to clean the first plurality of substrates.
In another aspect, a method of the invention cleans a plurality of disc-shaped substrates using megasonic wave energy. In accordance with this method, a plurality of substrates are immersed in a cleaning solution while megasonic wave energy is applied. After the substrates have been subjected to the cleaning solution and megasonic wave energy for a sufficient amount of time to produce substantial cleaning, the cleaning solution is dumped from the chamber.
The invention also provides an apparatus for cleaning disc-shaped substrates and reusing a chemical cleaning solution. The apparatus includes a chamber sized for receiving a plurality of substrates to be cleaned, the chamber having an outlet in its base for draining liquids therefrom. A plenum is located beneath the base of the chamber for receiving liquids drained from the chamber. The plenum has at least two outlets in its base. Each of the outlets in fluid communication with a holding tank. Further, the apparatus includes a recycle system for at least the chemical solution in one of the holding tanks. The recycle system includes an analyzer for chemical analysis of liquid in the holding tank, and a particle detector for detection of particulates in the liquids in the holding tank. The recycle system also includes a pump capable of recycling liquid from the holding tank to the cleaning chamber for cleaning the substrates.
In accordance with the invention, there is also presented a unique cleaning chamber that includes several features. Among these features are that the container is sized to contain a plurality of spaced apart disc-shaped substrates arranged in a horizontal stack for cleaning, and the container is sufficiently deep so that the substrates may be immersed in liquids within the container, when the container is in use. The container has an inner surface that is resistant to corrosive chemicals used in cleaning the substrates at temperatures in the range from about 60xc2x0 to 95xc2x0 C. Advantageously, the chamber may be equipped with a weir located adjacent its upper surrounding room, for receiving liquid spill over from the container, when the container is in use. Further, in one aspect of the container, the container has a V-shaped base (viewed from one end) converging to a central outlet duct that preferably extends along a substantial portion of the container. Inner surfaces of the container are preferably smooth and free of traps for retention of particulate contaminants and liquids, to allow rapid drainage and cleaning of the interior of the chamber.
In another aspect of the invention, there is presented an apparatus for holding a plurality of disc-shaped substrates in a horizontal stack, in spaced apert face-to-face relationship. The apparatus includes at least a base and a pair of upper parallel rods, of substantially equal length, with opposite ends mounted to a common end plate. Each of the upper pair of rods have, on inboard sides, equidistantly spaced notches of sufficient width for insertion of an edge portion of a disc bearing, each notch of one of the pair of rods is in registration with a notch on the other of the pair of rods. As a result, discs placed in registered notches of the rods will be aligned substantially vertically. To assist in robotic handling of the disc holder, the holder may be equipped with a vertical handle, ideally located proximate the mid-point of the rods, with an upper end that is adapted for being grasped by an end effector of a robot.
The invention provides many advantages over the prior art, as will be more fully appreciated from a study of the Detailed Description Section, here below. Among the notable advantages are the capability to reuse chemicals and so reduce hazardous waste generation and disposal, while also reducing chemical costs. Moreover, if desired, in certain embodiments the entire apparatus can be contained within a single station with a relatively small footprint. In that event, the steps of cleaning, rinsing and drying may be carried out in a single cleaning chamber. Further, a robot may be employed to load and unload the cleaning station with substrates.